Top 15 Experiments on Growth in Plants

The following points highlight the top fifteen experiments on growth in plants. Some of the experiments are: 1. Study of Meristems 2. Determination of Regions of Cell Enlargement in Leaves, Stems and Roots 3. Measurement of Growth 4. Determination of Leaf Area Index (LAI); Leaf Area Ratio (LAR); Net Assimilation Rate (NAR) or Unit Leaf Rate (ULR); and Relative Growth Rate (RGR) and Others.

Experiment # 1

Study of Meristems:

Experiment:

Medium longitudinal microtomic sections are cut through the stem tip and root tip of some suitable herbaceous species and are observed under high power of microscope.

Observation:

The apical meristematic region, embryonic leaves, bud primordia, nodes and internodes are distinguished in case of stem tip and in root tip approximate limits of the regions of cell divisions, cell enlargement and cell maturation are distinguished (Figure 32).

Meristematic cells are usually isodiametric in shape, compactly set without evident intercellular spaces, have dense cytoplasm with small vacuoles and large prominent nuclei. Plastids are in pro-plastid stage, cell wall thin and homogeneous. A gradual change in shape and size is observed in the derivatives which ultimately form permanent cells.

Inference:

Cells responsible for growth can thus be distinguished in medium longitudinal sections of apical regions of roots and stems.

Experiment # 2

Determination of Regions of Cell Enlargement in Leaves, Stems and Roots:

Experiment:

One of the younger leaves of a rapidly developing suit­able plant is selected. Now with the help of a scale two sets of lines at right angles to each other are drawn with India ink so that the leaf is marked with squares of equal sizes (marking can also be done with the help of space marker disc).

In another set a suitable plant which has developed sufficiently to have at least two to three internodes is selected. The stem portions of the upper three internodes are marked with India ink with short horizontal lines spaced equally apart.

In a third set some seeds of suitable species are allowed to germinate in moist filter paper. One of the seedlings with a root about 2 cm lengths is selected and the entire root is marked with India ink with horizontal lines spaced equally apart and seedling is allowed to grow in a bottle (Figure 33).

Observation:

After about three days the leaf, stem and the root are re-measured considering the area of the squares in case of the leaf and dis­tances between two horizontal lines in case of stem and root.

Inference:

Measurement shows that maximum increase in area of the squares takes place along the edge of the leaves which indicate that meristems plate meristem are located along this region. In case of stem maxi­mum growth is found just above the nodes.

This growth is due to inter­calary meristem left behind by the apical meristem which goes ahead during development. In case of root maximum growth is found just below the apical region which is due to apical meristem.

It is observed that the distance between the first and the second line near the tip has not separated much by growth, and this includes the zone of cell division by apical meristem. But the distances between the lines behind the meristem zone increases maxi­mum amount due to growth by elongation and this includes the zone of cell elongation.

Still further behind this zone the distance between the lines again is not marked and this zone includes the cell maturation zone.

Experiment # 3

Measurement of Growth:

(а) An ordinary method of growth measurement:

The linear expansion growth of any organ of a plant, i.e., length or breadth or area can be measured with the help of a centimeter scale.

The expansion growth of plant organ, i.e., increase in length, breadth, area or volume can be measured at different developmental stages and at various intervals. The growth rate, i.e., the growth increment per unit time can also be calculated.

The elongation of root can be measured by any scale or graph paper. Slide calipers can be used for measurement of thickness or diameter of an organ. Volume changes can be estimated by water dis­placement method.

(b) Measurement of vertical growth by simple Auxanometer (Arc indicator):

The rate of growth can be conveniently measured by a standard simple instrument called arc indicator (Figure 34).

The instrument consists of a metallic sextant scale (in angular degrees) fitted to a vertical stand by means of arms which meet forming a right angle with each other.

At this end they are fixed to an axle fitted with a pulley. The axle holds a pointer which can move up and down on the sextant scale when the pulley rotates. A thread is wound on the groove of the pulley. One end of this thread is tied at the apex of a growing plant while from the other end hangs a suitable weight.

As the plant grows in height the pulley rota­tes by the downward movement of the weight. With the rotation of the axle the pointer moves on the sextant scale and this movement is pro­portional to the growth in height of the plant. By recording the movement of the pointer by angular degrees at particular intervals the growth rate of the plant can be measured.

One angular degree

In linear measurement one angular degree =

(c) Measurement of ver­tical growth by Drum Auxanometer:

This is a more complex instrument and gives more detailed idea of growth rates both during day and night (Figure 35).

It consists of a re­volving drum with a smoked paper pasted on it. The apical region of a growing potted plant is tied with one end of a thread which passes over a pulley holding a weight at the other end.

The pulley is fixed to a vertical stand:

Another thread passing over a bigger pulley holds a weight at one end while to-the other end, a pointer is fixed horizontally in such a way that only the sharp end of the pointer just touches the surface of smoked paper, and its course of movement can be traced on it.

As the shoot apex gr6ws in height the hanging weight pulls the pointer upward and as the drum rotates (once in every hour), the pointer traces its path along the smoked paper. The perpendicular distances between tracings on the drum indicate propor­tional hourly growth.

It should be noted that such distances are longer 4t night compared to day indicating increased growth during the hours of darkness. The result also indicates that a periodicity of growth exists in plants.

(d) Measurement of vertical growth by horizontal microscope:

The vertical increase in height of a shoot apex can also be measured with the help of an optical micros­cope. The optical tube of this micro­scope remains in horizontal position, (Figure 36).

The optical tube can be moved upward and downward with Horizontal the help of a screw and the vertical movement can be measured with the help of a linear scale attached to the stand.

Now a small point is made with ink on the shoot apex which is brought in focus by observing through the eyepiece of microscope. As the shoot apex grows in height the symbolic point also goes up and call again be observed through the microscope by moving the optical tube upward. The distance between initial and final reading at a particular interval of time gives the growth rate of a plant.

Experiment # 4

Determination of Leaf Area Index (LAI); Leaf Area Ratio (LAR); Net Assimilation Rate (NAR) or Unit Leaf Rate (ULR); and Relative Growth Rate (RGR):

(i) Leaf area index (LAI):

Leaf area index is the morphological index of plant form.

It may be determined in the following way:

Leaf area index (LAI) = N x La.

Where N = number of plants per square metre of the ground area and hence the area of the ground per plant is 1/N. The leaf area divided by this area) gives the LAI which is a pure number. La can be determined in field condition by constant multiplying method as follows. Actual areas of different leaves of the plant are deter­mined individually by graph paper method and average of them is calculated. Let it be a.

Again areas of these leaves are individually determined by multiplying their length and breadth and average of them is calculated. Let it be b. Now a/b may be taken as a constant (K). Thus to get the area of any leaf of a plant roughly, its length is first multiplied by its breadth and then with the constant K.

(ii) Leaf area ratio (LAR):

Leaf area ratio gives an indication of the dry matter accumulation by the leaf in relation to its area.

It may be determined in the following way:

Where LA = Area of a leaf

LW = Total dry weight of the leaf

(iii) Net assimilation rate (NAR) or Unit leaf rate (ULR):

This is a physiological index (rate of increase of dry weight of the whole plant per unit leaf area) closely connected with the photosynthetic activity of the leaves.

It relates dry weight increase, which in most plants has carbon assimilation as its most important components, to the area of those organs most concerned with carbon assimilation, i.e., leaves.

It may be deter­mined in the following way:

(iv) Relative growth rate (RGR):

This indicates the overall growth index, i.e., the growth taking place in the plant daily and may be determined as follows:

Experiment # 5

Demonstration of Seasonal Periodicity in Growth of Woody Perennials:

Experiment:

This experiment should be performed in four different seasons of the year, viz., spring season (February to April), summer season (May to July), rainy season (August to October) and winter season (Novem­ber to January).

At the beginning of the spring season several branches on a young tree or shrub are selected and buds on each are tagged.

The diameter of each branch at the base is measured. The length of each deve­loping bud is also measured. This measurement is continued at an interval of 10 days throughout four seasons. The average of the measurement of each season is recorded.

Results:

The results are plotted taking average increase in growth per 10 days in each season as an abscissa and days (90) in each season as ordinate.

Discussion:

The experiment shows that there exists a seasonal variation in growth pattern in plants. The maximum increase in growth takes place during the growing season, i.e., the spring and this decrease to a minimum during the lean months of the winter season.

Experiment # 6

Demonstration of Growth Correlation:

Experiment:

Three uniform sized leaves of Bryophyllum are taken. Now narrow transverse strips are cut from one leaf through the midrib allowing the leaf to remain attached near the margins. Again narrow transverse strips are cut from the second leaf allowing the midrib to remain intact. The third leaf is also cut transversely into a number of segments through the lobes and not through the notches (Figure 37).

Each leaf is placed on moist filter paper in a covered petridish and kept out of direct sunlight. One control leaf is also placed in another petridish. Filter papers are remoistened from time to time.

Results:

After four weeks the number, height and position of new plants growing from the notches in the margin of the leaves are recorded and compared.

Discussion:

The abilities of one part of the plant to direct growth and development in another are called correlation effects. Tip of the leaf is necessary for perception of stimulus but not for the response which takes place further down the tip.

In the present experiment the tip is com­pletely separated from the other parts in third leaf. In second leaf the notches are separated where the mid-vein is the connecting link between different parts of leaf. Whereas in case of first leaf the notches are directly connected with the tip.

It is observed that maximum number of normal plants (less than control) appear in case of the first leaf, then in second and minimum in third.

Experiment # 7

To Show the Root/Shoot Ratio at Various Experimental Conditions:

Experiment:

Four pots containing washed sand are taken. Ten seedlings (Vigna or Phaseolus) of uniform size and age are transplanted in each pot. One pot is placed in bright light, the second in shade, the third is treated with 10 ml of calcium nitrate (concentration 0.820 mg/litre Ca(NO₃)₂) solution and the fourth is treated with 1 ml of this calcium nitrate solution.

Results:

The growth of plants in each pot is observed over a period of 10 to 15 days. At the termination of the experiment the shoot and root portions are separated and fresh weights are taken after cutting the shoots and roots into small pieces.

The shoots and roots are then dried at 100°C in an oven for 72 hours and these are reweighed to determine the dry weight of each. The ratio of root to shoot for each treatment is cal­culated on both fresh and dry weight basis and results are tabulated.

Discussion:

The root by shoot ratio is higher in plants grown in light compared to plants grown in shade. Again the root by shoot ratio is higher in plants grown in low nitrogen level compared to those grown in high nitrogen level.

In fact the effect of a given treatment is likely to favour root growth relative to that of shoot or vice-versa, is decided by the concen­tration of various other essential factors such as organic food, light, hor­mones, minerals, oxygen, water content, etc., which often limit to a greater degree the process of growth.

Experiment # 8

Demonstration of Grand Period of Growth:

Experiment:

This experiment may be performed taking growth rate of root tip or of any suitable plant, or unicellular organism.

A fair number of plants grown under favourable conditions in open atmosphere may be used for taking growth data. Increase in height of the plant is recorded at an interval of seven days from germination until increase in height ceases.

Results:

The recorded results are graphically plotted taking time (weeks) as abscissa and increase in length or height as ordinate.

Discussion:

In case of root growth it is observed that the root tip first grows slowly then rapidly, and finally slowly until it stops elongation. Such changes constitute the grand period of growth and a curve resembling that ob­tained for a single root may be obtained for an entire plant.

In case of shoot growth the rate of growth gives a similar rise and fall whereas total height of plant of course does not drop. The curve (Figure 38) will be of “S” shape (sigmoid curve). The growth of the entire plant or of the plant organ characteristically passes through the stages represented by this curve the time during which this occurs is called the grand period of growth.

Experiment # 9

Demonstration of the Effect of Water Supply on Growth of Plant:

Experiment:

Four suitable potted plants are taken and are allowed to become dry so that the plants just start to wilt. One pot is watered to optimum, second to maximum, third to minimum and the fourth is kept as control (not watered). The growth rate is measured with the help of auxanometer.

Results:

The growth rates of each potted plant is separately taken and graphically represented.

Discussion:

Maximum growth is observed in optimum watered plant which is followed by maximum watered, minimum watered and the plant of the fourth pot, which has not been watered at all, wilts. Water is essential for normal growth of all plants.

All living tissues contain some water, and more active tissues such as leaves, growing roots and stems rarely con­tain less than 50% water. Growth inhibitions are induced by wilting due to closure of stomata and inhibition of photosynthesis.

Heavy watering of the pots interferes with the aeration of roots due to water logging. Hence growth rate is inhibited.

N.B. This experiment may also be performed with fruiting tomato plants or other fleshy-fruited plants if available in pots. The effect of water upon the rate of growth of fruit (measured in terms of diameter of fruits) may be observed.

Experiment # 10

Demonstration of Effect of Light on Plant Growth:

Experiment:

Two suitable well-watered potted plants are selected. One pot is kept under bright sunshine (or under artificial light—200 W bulb fitted with a reflector at a distance of 3 to 4 feet from the plant). The other is kept in shade. The growth rates of the plants arc measured with the help of an auxanometer.

Results:

The growth rates are graphically plotted.

Discussion:

The growth rates will be higher in plant kept in light compared to the plant kept in shady place. The rate of growth is higher under optimum height intensity whereas the effect of high light intensity is in general retarding on growth process.The effect of light is mainly through photosynthesis and transpiration. The effect is also interrelated with the effect of temperature and water.

N.B. Dark-grown seedlings sometimes show higher growth rate (in height) compared to light-grown ones. However, dry weight increase is more in case of the latter.

Experiment # 11

Demonstration of the effect of Temperature on Plant Growth:

Experiment:

This experiment can be performed by recording the growth rates of roots or shoots kept under different temperatures.

Two suitably grown well watered plants are taken. One is kept at a temperature of 20°C and the other at 30°C under well illuminated condition. The grow A rate is measured at an interval of 7 days in 4 to 5 weeks in terms of dry weight and fresh weight of the plants.

Results:

The growth rates of the plant under two different tempe­ratures are graphically plotted.

Discussion:

The growth rate increases with increase in temperature within a particular range (25 to 35°C.). Both High and low temperatures inhibit growth. The effect of temperature on growth is generally con­trolled enzyme activity. Each of the physiological process is directly or indirectly influenced by varying degrees of temperature.

Experiment # 12

Demonstration of Effect of Oxygen on Plant Growth:

Experiment:

Two 100 ml rubber-stoppered bottles are taken. To one bottle 2 gms of pyrogallic acid and 10 gms of KOH in 60 ml of water are added. The bottle is shaken well.

The oxygen within the bottle will be absorbed by it. The alkaline pyrogallate solution is thrown off and stoppered carefully. The radicles of two or three germinating seedlings are marked with India ink and kept in two petridishes containing water.

The oxygen free bottle is held inverted covering the seedlings of one petridish. The seedlings of the other petridish are similarly covered with the other bottle. The growth rate is measured in each case.

Results:

The changes in growth rates are graphically plotted in each case and compared.

Discussion:

The rate of growth of radicle will be higher in seedlings covered with bottle containing normal air compared to the bottle containing oxygen-free air. Oxygen in molecular form plays an important role in growth phenomena chiefly through the influence on respiration.

Usually a depletion of oxygen is associated with an increase in carbon dioxide and this may further depress the root growth as well as salt and water absorption. In plant growth porosity of soil is of major importance in influencing the aeration and, therefore, the oxygen supply to roots.

Experiment # 13

Demonstration of Effect of Food Supply on Growth:

Experiment:

Some rice and bean seeds are separately grown. The seedlings are taken when the roots are 2 to 3 cm long. Root tips are marked with India ink as in the previous experiment. Half of the endosperm tissue from some rice seedlings and half of the cotyledonary tissue from bean seedlings are removed with the help of a sharp knife.

The remaining seedlings with intact endosperms and cotyledons are kept as control. The mutilated and control seedlings are kept together in petridishes under favourable conditions.

Results:

The growth rates of roots of mutilated and control seedlings are measured in centimeters over a period of four days and graphically represented.

Discussion:

The endosperm in case of rice and cotyledons in case of beans are the reservoir of food materials which nourish the growing seed­lings up to certain stage of development after which they can independently synthesize their food by photosynthesis with developing leaves.

If the food supply is partly reduced by removing a portion of endosperm or cotyledon before the plant becomes independent the growth is hampered due to paucity of food supply.

N.B. This experiment may also be performed by growing half of the independently growing seedlings in dark and half in light. The growth rate in terms of fresh and dry weights may be measured and compared.

Experiment # 14

Demonstration of Influence of Fruiting Upon Vegetative Growth of Plant:

Experiment:

Some suitable fruit plants, e.g., tomato, cotton, etc. are grown in field plots under natural environment. The growth data of the plant, e.g., height and branch length are taken when the flower buds just appear.

Flowers and young fruits are regularly removed from half of the plants as soon as they appear. When the fruits have developed to a certain degree of maturity in the other half of plants the final height and branch length of all the plants are recorded.

Results:

The differences in vegetative growth between the plants on which fruiting occurs and those on which fruiting is prevented are graphi­cally (histogram) plotted and compared.

Discussion:

The vegetative growth of the plant almost ceases when flowers and fruits appear on it. Flowers and fruits are active mobilisation centres which draw the metabolites from other parts of the plants leading to the reduction of vegetative growth. The removal of flowers and fruits from the plants removes the mobilisation centres keeping the plant in vegetative condition.

Experiment # 15

Demonstration of the Effect of Rest Period on Growth:

Experiment:

One lot of freshly collected potato tubers and one lot of one year old potato tubers are taken for this experiment. The tubers are cut into pieces keeping the eyes intact. These are then allowed to grow in pots.

Observation:

It is observed that freshly harvested potato tubers fail to sprout whereas one-year-old tubers sprout normally.

Inference:

The rest period is attributed to some condition within the plants or its structures. Perfectly viable seeds or buds having rest periods are characterized by the failure of germination or sprouting even when placed under environmental conditions that are ordinarily favourable for quick germination and vigorous seedling growth.

As soon as the rest period is over such seeds or buds readily germinate or sprout. The possible reasons for rest period are unfavourable environment, inhibitor promoter level, deficiency of nitrogen, photoperiod, concentration of auxin and ethylene, etc.